Protein kinases represent a large family of enzymes, which catalyze the phosphorylation of target protein substrates. The phosphorylation is usually a transfer reaction of a phosphate group from ATP to the protein substrate. Common points of attachment for the phosphate group to the protein substrate include, for example, a tyrosine, serine or threonine residue. For example, protein tyrosine kinases (PTKs) are enzymes, which catalyze the phosphorylation of specific tyrosine residues in cellular proteins. Examples of kinases in the protein kinase family include, without limitation, ab1, Akt, bcr-ab1, Blk, Brk, Btk, c-kit, c-Met, c-src, c-fms, CDK1, CDK2, CDK3, CDK4, CDK5, CDK6, CDK7, CDK8, CDK9, CDK10, cRaf1, CSF1R, CSK, EGFR, ErbB2, ErbB3, ErbB4, Erk, Fak, fes, FGFR1, FGFR2, FGFR3, FGFR4, FGFR5, Fgr, flt-1, Fps, Frk, Fyn, Hck, IGF-1R, INS-R, Jak, KDR, Lck, Lyn, MEK, p38, PDGFR, PIK, PKC, PYK2, ros, Tie, Tie-2, TRK, Yes, and Zap70. Due to their activity in numerous cellular processes, protein kinases have emerged as important therapeutic targets.
Protein kinases play a central role in the regulation and maintenance of a wide variety of cellular processes and cellular function. For example, kinase activity acts as molecular switches regulating cell proliferation, activation, and/or differentiation. Uncontrolled or excessive kinase activity has been observed in many disease states including benign and malignant proliferation disorders as well as diseases resulting from inappropriate activation of the immune system (autoimmune disorders), allograff rejection, and graft vs host disease. In addition, endothelial cell specific receptor PTKs, such as VEGF-2 and Tie-2, mediate the angiogenic process and are involved in supporting the progression of cancers and other diseases involving uncontrolled vascularization.
Angiogenesis is the process of developing new blood vessels, particularly capillaries, from pre-existing vasculature and is an essential component of embryogenesis, normal physiological growth, repair, and tumor expansion. Angiogenesis remodels small vessels into larger conduit vessels, a physiologically important aspect of vascular growth in adult tissues. Vascular growth is required for beneficial processes such as tissue repair, wound healing, recovery from tissue ischemia and menstrual cycling.
Certain diseases and/or pathological conditions develop as a result of, or are known to be associated with, the regulation and/or deregulation of angiogenesis. For example, ocular neovascularisation such as retinopathies (including diabetic retinopathy), age-related macular degeneration, psoriasis, hemangioblastoma, hemangioma, and arteriosclerosis have been found to be caused, in part, due the loss of regulation and/or maintenance of vascular growth. Inflammatory diseases such as a rheumatoid or rheumatic inflammatory disease, and especially arthritis (including rheumatoid arthritis) where new capillary blood vessels invade the joint and destroy cartilage, have been associated with angiogenesis. In addition, chronic inflammatory disorders such as chronic asthma, arterial or post-transplantational atherosclerosis, endometriosis, and neoplastic diseases including so-called solid tumors and liquid tumors (for example, leukemias), have been found to be linked to the regulation and control of angiogenesis.
The involvement of angiogenesis in major diseases has led to the identification and development of various targets for inhibiting angiogenesis. These targets relate to various receptors, enzymes, and other proteins in the angiogenic process or cascade of events leading to angiogenesis, such as, for example, activation of endothelial cells by an angiogenic signal, synthesis and release of degradative enzymes, endothelial cell migration, proliferation of endothelial cells, and formation of capillary tubules.
One target identified in the cascade of events leading to angiogenesis is the Tie receptor family. The Tie-1 and Tie-2 receptors are single-transmembrane, tyrosine kinase receptors (Tie stands for tyrosine kinase receptors with immunoglobulin and EGF homology domains). Tie-2 is an endothelial cell specific receptor tyrosine kinase, which is involved in angiogenic processes, such as vessel branching, sprouting, remodeling, maturation and stability. Tie-2 is the first mammalian receptor for which both agonist ligand(s) (for example, Angiopoietin-1 (“Ang1”) which binds to and stimulates phosphorylation and signal transduction of Tie-2), and context dependent agonist/antagonist ligand(s) (for example, Angiopoietin-2 (“Ang2”)) have been identified. Knock out and transgenic manipulation of the expression of Tie-2 and its ligands indicates that tight spacial and temporal control of Tie-2 signaling is important for the proper development of new vascularization.
Biological models suggest that the stimulation of Tie-2 by the Ang1 ligand is directly involved in the branching, sprouting and outgrowth of new vessels, and recruitment and interaction of periendothelial support cells important in maintaining vessel integrity and inducing quiescence. The absence of Ang1 stimulation of Tie-2 or the inhibition of Tie-2 autophosphorylation by Ang2, which is produced at high levels at sites of vascular regression, may cause a loss in vascular structure and matrix contacts resulting in endothelial death, especially in the absence of growth/survival stimuli.
Recently, upregulation of Tie-2 expression has been found in the vascular synovial pannus of arthritic joints of humans, consistent with the role in inappropriate neovasculariation. This finding suggests that Tie-2 plays a role in the progression of rheumatoid arthritis. Point mutations producing constitutively activated forms of Tie-2 have been identified in association with human venous malformation disorders. Tie-2 inhibitors would, therefore, be useful in treating such disorders, as well as in other instances of improper neovasacularization. However, with the recent recognition of Ang3 and Ang4 as additional Tie-2 binding ligands, targeting a Tie-2 ligand-receptor interaction as an anti-angiogenic therapeutic approach is less favorable. Accordingly, a Tie-2 receptor kinase inhibition approach has become the strategy of choice.
Angiogenesis is regarded as an absolute prerequisite for tumors that grow beyond a diameter of about 1-2 mm. Up to this size, oxygen and nutrients may be supplied to the tumor cells by diffusion. Every tumor, regardless of its origin and its cause, is thus dependent on angiogenesis for its growth after it has reached a certain size.
Three principal mechanisms play an important part in the activity of angiogenesis inhibitors against tumors: 1) Inhibition of the growth of vessels, especially capillaries, into vascular resting tumors, with the result that there is no net tumor growth owing to the balance that is achieved between cell death and proliferation; 2) Prevention of the migration of tumor cells owing to the absence of blood flow to and from tumors; and 3) Inhibition of endothelial cell proliferation, thus avoiding the paracrine growth-stimulating effect exerted on the surrounding tissue by the endothelial cells which normally line the vessels. See R. Connell and J. Beebe, Exp. Opin. Ther. Patents, 11:77-114 (2001).
The inhibition of vascular growth in this context has also shown beneficial effects in preclinical animal models. For example, inhibition of angiogenesis by blocking vascular endothelial growth factor or its receptor has resulted in inhibition of tumor growth and in retinopathy. Also, the development of pathological pannus tissue in rheumatoid arthritis involves angiogenesis and might be blocked by inhibitors of angiogenesis.
The ability to stimulate vascular growth has potential utility for treatment of ischemia-induced pathologies such as myocardial infarction, coronary artery disease, peripheral vascular disease, and stroke. The sprouting of new vessels and/or the expansion of small vessels in ischemic tissues prevents ischemic tissue death and induces tissue repair. Regulating angiogenesis by inhibiting certain recognized pathways in this process would, therefore, be useful in treating diseases, such as ocular neovascularization, including retinopathy, age-related macular degeneration, psoriasis, hemangioblastoma, hemangioma, arteriosclerosis, inflammatory disease rheumatoid arthritis, chronic inflammatory disorders such as chronic asthma, arterial or post-transplantational atherosclerosis, endometriosis, and neoplastic diseases such as leukemias, otherwise known to be associated with deregulated angiogenesis. Treatment of malaria and related viral diseases may also be mediated by HGF and cMet.
Recent work on the relationship between inhibition of angiogenesis and the suppression or reversion of tumor progression shows great promise in the treatment of cancer (Nature, 390:404-407 (1997)), especially the use of multiple angiogenesis inhibitors compared to the effect of a single inhibitor.
Non-receptor tyrosine kinases represent a collection of cellular enzymes, which lack extracellular activity and transmembrane sequences. Examples of non-receptor tyrosine kinases identified include over twenty-four individual kinases, comprising eleven (11) subfamilies (Src, Frk, Btk, Csk, Abl, Zap70, Fes/Fps, Fak, jak, Ack, and LIMK). Src is thought to be the largest family including Src, Lck, Fyn(B), Fyn(T), Lyn, Yes, Hck, Fgr and Blk (for review see: Bolen, J B, and Brugge, J S Annu. Rev. Immunol, 15, 371, 1997). The Src subfamily has been linked to oncogenesis and immune responses (See Bohlen, Oncogene, 8:2025-2031, 1993). These kinases have also been found to be involved in cellular signaling pathways in numerous pathogenic conditions, including cancer, psoriasis, and other hyper-proliferative disorders or hyper-immune responses. Thus, it would be useful to inhibit the activity of non-receptor kinases as well.
Members of the Src-family of tyrosine kinases, in particular, have been shown to be important in cell signal transduction as it relates to inflammatory response and inflammation-related conditions. Gene disruption studies suggest that inhibition of some members of the src family of kinases would potentially lead to a therapeutic benefit. Src(−/−) mice have abnormalities in bone remodeling or osteopetrosis (Soriano, P. Cell 1991, 64, 693), suggesting that inhibition of this kinase might be useful in diseases of bone resorption, such as osteoporosis. Lck(−/−) mice have defects in T cell maturation and activation (Anderson, S J et al. Adv. Immunol. 1994, 56, 151), suggesting that inhibition of this kinase might be useful in diseases of T cell mediated inflammation. In addition, human patients have been identified with mutations affecting Lck kinase activity (Goldman, F D et al. J. Clin. Invest. 1998, 102, 421). These patients suffer from a severe combined immunodeficiency disorder (SCID).
T cells play a pivotal role in the regulation of immune responses and are important for establishing immunity to pathogens. In addition, T cells are often activated during inflammatory autoimmune diseases, such as rheumatoid arthritis, inflammatory bowel disease, type I diabetes, multiple sclerosis, Sjogren's disease, myasthenia gravis, psoriasis, and lupus. T cell activation is also an important component of transplant rejection, allergic reactions, and asthma.
T cells are activated by specific antigens through the T cell receptor (TCR), which is expressed on the cell surface. This activation triggers a series of intracellular signaling cascades mediated by enzymes expressed within the cell (Kane, L P et al. Current Opinion in Immunol. 12, 242, 2000). These cascades lead to gene regulation events that result in the production of cytokines, like interleukin-2 (IL-2). IL-2 is a necessary cytokine in T cell activation, leading to proliferation and amplification of specific immune responses.
Src-family kinases are also important for signaling downstream of other immune cell receptors. Fyn, like Lck, is involved in TCR signaling in T cells (Appleby, M W et al. Cell, 70, 751, 1992). Hck and Fgr are involved in Fcγ receptor signaling leading to neutrophil activation (Vicentini, L. et al. J. Immunol. 2002, 168, 6446). Lyn and Src also participate in Fcγ receptor signaling leading to release of histamine and other allergic mediators (Turner, H. and Kinet, J-P Nature 1999, 402, B24). These-findings suggest that Src family kinase inhibitors may be useful in treating allergic diseases and asthma.
Src kinases are also activated in tumors including sarcoma, melanoma, breast, and colon cancers suggesting that Src kinase inhibitors may be useful anti-cancer agents (Abram, C L and Courtneidge, S A Exp. Cell Res., 254, 1, 2000). Src kinase inhibitors have also been reported to be effective in an animal model of cerebral ischemia (R. Paul et al. Nature Medicine, 7, 222, 2001), suggesting that Src kinase inhibitors may be effective at limiting brain damage following stroke.
Many classes of compounds have been disclosed to modulate or, more specifically, inhibit kinase activity for use to treat kinase-related conditions or other disorders. For example, the PCT publication, WO 01/81311, published on Nov. 1, 2001, describes substituted benzoic acid amides and use thereof for the inhibition of angiogenisis; U.S. Pat. No. 6,440,965, issued Aug. 27, 2002, describes substituted pyrimidine derivatives and their use in the treatment of neurodegenerative or neurological disorders of the central nervous system; PCT publication, WO 02/08205, published on Jan. 13, 2001, describes substituted pyrimidines having neurotrophic activity; PCT publication, WO 03/014111, published on Feb. 20, 2003, describes arylpiperazines and arylpiperidines and their use as metalloproteinase inhibiting agents; PCT publication, WO 03/024448, published on Mar. 27, 2003, describes compounds as inhibitors of histone deacetylase enzymatic activity; PCT publication, WO 04/058776, published on Jul. 15, 2004, describes compounds which possess anti-angiogenic activity; and PCT publication, WO 04/062601, published on Jul. 29, 2004, describes compounds as anti-bacterial agents for generally treating infections caused by gram-negative bacteria.